The former China international, who is now 38, joined United in 2004 from Chinese side Dalian Shide. He became the club&aposs first-ever East Asian player.
Dong joined the Reds for an initial fee of 500,000, which could have risen to 3.5million, depending on the number of appearances he made for the Reds. He was not initially allowed to play for the first team because he was ineligible for a work permit.
As a result, the former striker, who last played back in 2014, was farmed out on loan to Royal Antwerp, spending two seasons at the Belgian club. He scored 34 goals in 57 games.
Following initial issues obtaining a work permit, Dong made his competitive debut for United in May 2007, starting a 0-0 draw with Chelsea in the Premier League. He started in attack alongside former United manager Ole Gunnar Solskjaer.
He made just two more appearances for United, starting a shock 2-0 defeat to Coventry City in the League Cup in September the same year before appearing as a substitute in a Champions League clash with Roma three months later.
Dong left the club in August 2008 after he and United mutually agreed to terminate his contract. He returned to former club Dalian Shide and later returned to Europe with Legia Warsaw in 2010.
Back at Old Trafford on Saturday, United confirmed he was in attendance ahead of kick-off, posting a picture of him walking in front of the Sir Bobby Charlton Stand on their X account. United posted: “Good to see you again, Dong.”